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Fixation Augmentation Techniques: When and How

AAOS Chicago March 26, 2006
Management of Osteoporotic Wrist Fractures
8AM-10AM

A MORONI, MD

Professor of Orthopaedic Surgery
Rizzoli Orthopaedic Institute
University of Bologna
Bologna, Italy
a.moroni@ior.it

I. What are fixation augmentation techniques?

Fixation augmentation techniques can be defined as surgical procedures aimed at increasing implant stability. These techniques include a variety of materials such as: polymethylmethacrylate (PMMA), bone grafts, calcium phosphate ceramics including blocks, cements, and coatings and modified implants. Recently innovative “pharmaceutical” augmentation concepts such as bisphosphonates have also been introduced.

Although the fracture healing potential in the osteoporotic wrist fracture patient is normal, the incidence of fracture malunion and consequently poor functional outcome is significant. This is due to the inability of the implant to maintain the surgical reduction for the period of time required for the completion of the fracture-healing process. With osteoporotic wrist fracture fixation, in particular in metaphyseal cancellous bone, there is poor screw purchase in the mechanically-weak bone.

When managing fragility fractures, the diagnosis of osteoporosis is the first hurdle that the orthopaedic surgeon encounters. Among the several diagnostic tools available, dual energy x-ray absorptiometry (DXA) scanners have been identified as the gold standard since 1994 by the World Health Organization. Regrettably, when treating elderly fracture patients, the use of DXA scanners prior to surgery is not common practice. This imposes a limitation for the orthopaedic surgeon who is lacking crucial data concerning patient bone quality. Knowing patient bone quality prior to surgery would be useful not only for the administration of the correct medical therapy which is effective for secondary fracture prevention but also for selecting the correct surgical treatment, including the use of fixation augmentation techniques. When treating wrist fractures in patients over 65 years old, DXA of the contralateral wrist should be taken prior to surgery.

Existent problems focus on the implant in retaining good fixation at the bone-screw interface. Currently, there are no implants specifically-designed for osteoporotic bone fixation. All the available implants, including screws are designed for normal healthy bone.

II. When to use fixation augmentation techniques?

Osteoporotic bone (DXA BMD T-Score < -2.5 SD)
Mechanically weak bone

III. What is the role of fixation augmentation techniques?

A. Advantages

• Structural support
• Improved fixation
• Improved fracture stability
• Early recovery
• Reduced morbidity
• Reduced complications

IV. Classification

1. PMMA
2. Bone grafts
3. Calcium phosphate cement
4. Calcium phosphate blocks
5. Calcium phosphate coatings
6. Modified implants
7. Innovative concepts

1. PMMA

• Technically-demanding
• Time consuming
• Increased cost
• Complications
• Risk of inhibiting fracture healing
• Difficult removal

Technique # 1

• Drill hole
• Fill with PMMA
• Allow to set
• Re-drill hole
• Tap and implant screw

Technique #2

• Drill hole
• Fill with PMMA
• Implant screw before cement sets

  

2. Bone grafts

Autografts

• Enhances osteogenic response
• Generally harvested from patient’s iliac crest
• Same biological potential as normal healthy bone
• Increased morbidity

Allografts

• Mechanical potential for improved fracture stability
• Used opposite to the plate for improved screw purchase
• No donor-site morbidity
• Theoretical possibility for disease transmission Prospective randomized study of 17 unstable distal forearm fractures (Herrera)
• Cancellous allograft and external fixation
• Results: 3 excellent; 8 good; 6 fair
• Cancellous bone allograft is a useful adjunct to external fixation

3. Calcium phosphate cement

Advantages

• Injectable
• Non-exothermic
• Structural support
• Compressive strength higher than cancellous bone
• No morbidity
• Good bone penetration
• No adverse biological effects

Burning Issues

• Remodelling capacity?
• Resorption?
• Mechanical strength?
• Long-term effects?
• Cost effective compared to the standard treatment?
• Reducing the need for external & internal fixation?
• Reducing healing time?

Prospective Randomized Study (Sanchez-Sotelo)

• 110 patients
  –55 cast
  –55 Norian SRS and cast for 2 weeks
• Outcome: Function
  –Norian SRS      82% satisfactory
  –Cast      56% satisfactory
• Radiologic
  –Norian      18% malunion
  –Cast      42% malunion

  

Prospective randomized study (Cassidy)

• Clinical differences at six and eight weeks postop
• Three months, differences had normalized except for digital motion (better in Norian SRS treatment group)
• Cement in extraosseous locations in 70%
• Loss of reduction in 37%
• Extraosseous material disappeared in 83/112 patients in 1 year

Highlights

• CP cement alone without additional fixation is not satisfactory for metaphyseal bone defects in wrist fractures

4. Hydroxyapatite granules/blocks

• High and low crystallinity mixture of hydroxyapatite
• Slow resorption
• Osteointegration
• Low mechanical strength
• Dynamic external fixation: 24/25 excellent; HA block better than granules (Sakano)
• Results comparable to those obtained with autografts with substantial cost savings (Wolf)

5. Hydroxyapatite coatings

• Optimal fixation and osteointegration ability with hydroxyapatite-coated screws
• Reduced incidence of screw loosening
• Reduced incidence of pin-track infection

Prospective randomized study – (Moroni)

• 20 female patients with osteoporosis and wrist fracture treated with external fixation
• Randomized to receive either standard tapered pins or hydroxyapatite-coated tapered pins.

Mean extraction torque:

• Lower than the corresponding insertion torque at each pin position in the group treated with standard pins (p < 0.05)
• Higher than the corresponding insertion torque at each pin position in the group managed with hydroxyapatite-coated pins (p = 0.001).
• Good fixation with HA coated pins regardless of pin insertion torque
• Pin-track infection:
  2 patients with standard pins
  0 patients with HA-coated pins
• No difference in pain at pin removal

6. Modified Implants

Screw design

• Smaller pitch
• Greater screw thread angle
• Smaller core diameter
• Interlocking screw
• Expandable screw

Implant design

• IM implants
• Fixed angle plates

  

7. Innovative concepts

Peptide Signaling Molecules

Thrombin peptides

• Acceleration of fracture repair by increasing the rate of tissue revascularization.
• Quantitative histology from rat fracture callus 21 days after treatment indicated that fractures treated with TP508 had significantly more large functional blood vessels than controls.

Osteoinductive Molecules

• Osteogenic protein-1 (OP-1, BMP-7)
• Bone Morphogenic Protein-2 (BMP-2)
• Potential for increased local bone density
• Potential for accelerated fracture healing

Pharmacological Agents

• Bisphosphonates (Alendronate, Ibandronate, Zolendronic Acid)
• PTH
• Animal studies have shown that bisphosphonates can improve early screw fixation in both cortical and cancellous bone (Skoglund, Miyahi)

Combined Strategies

• Cements loaded with osteoinductive growth factors, cells and drugs
• Coated fracture fixation implants loaded with osteoinductive growth factors, cells and drugs

References:

1. Cassidy C, Jupiter JB, Cohen M, Delli-Santi M, Fennell C, Leinberry C, Husband J, Ladd A, Seitz WR, Constanz B: Norian SRS cement compared with conventional fixation in distal radial fractures. A randomized study. J Bone Joint Surg Am 2003; 85-A (11): 2127-2137.
2. Herrera M, Chapman CB, Roh M, Strauch RJ, Rosenwasser MP.Treatment of unstable distal radius fractures with cancellous allograft and external fixation. J Hand Surg 1999. 24 (6): 1269-78
3. Kofoed H. Comminuted displaced Colles’fractures. Treatment with intramedullary methylmethacrylate stabilization. Acta Orthop Scand. 1983; 54 (2): 307-11.
4. Larsson, S. Treatment of osteoporotic fractures. Scand J Surgery 2002; 91: 140-146.
5. Miyaji T, Nakase T, Azuma Y, Shimizu N, Uchiyama Y, Yoshikawa H: Alendronate inhibits bone resorption at the bone-screw interface. Clin Ortho Relat Res 2005; 430: 195-201.
6. Moroni, A, Hoang-Kim, A, Lio, V, Giannini, S. Current Augmentation Fixation Techniques for the Osteoporotic Patient. Scand J Surgery 2005 94: 1-00, 2005.
7. Moroni A, Faldini C, Marchetti S, Manca M, Consoli V, Giannini S. Improvement of the bone-pin interface strength in osteoporotic bone with use of hydroxyapatite-coated tapered external fixation pins. A prospective, randomized clinical study of wrist fractures. J Bone Joint Surg Am 2001: 83-A (5): 717-721.
8. Sakano H, Koshino T, Takeuchi R, Sakai N, Saito T. Treatment of the unstable distal radius fracture with external fixation and a hydroxyapatite spacer. J Hand Surg 2001 26 (5). 923-930.
9. Sanchez-Sotelo J, Munuera L, Madero R. Treatment of fractures of the distal radius with a remodellable bone cement: a prospective, randomized study using Norian SRS. J Bone Joint Surg [Br] 2000 82 (6): 856-63.
10. Schmalholz A. External skeletal fixation versus cement fixation in the treatment of redislocated Colles’ fracture. Clin Orthop Relat Res 1990; (254): 236-41.
11. Skoglund B, Holmertz J, Aspenberg P: Systemic and local ibandronate enhance screw fixation. J Orthopaedic Research 2004; 22: 1108-1113.
12. Stromse, K. Fracture fixation problems in osteoporosis. Injury 2004; 35 (2), 107-113.
13. Wolf SW, Pike L, Slade JF III, Katz LD: Augmentation of distal radius fracture fixation with coralline hydroxyapatite bone graft substitute. J Hand Surg Am 1999; 24: 816-827.
14. Zimmerman R, Gabl M, Lutz M, Angermann P, Gschwenter M, Pechlaner S. Injectable calcium phosphate bone cement Norian SRS for the treatment of intra-articular compression fractures of the distal radius in osteoporotic women. Arch Orthop Trauma Surg 2003; 123: 22-27.